1. Field of the Invention
This invention pertains to medical catheters, and more particularly to catheters adapted for transcutaneous or complete implantation in the body of a human patient, thereby to provide access through the catheter to the cardiovascular system of the patient.
2. State of the Art
Catheters are commonly used to access the cardiovascular system of a patient from outside the body of the patient. The cardiovascular access afforded by such catheters permits the monitoring of blood pressure, the aspiration of blood, and the infusion of medicaments and nutrients at various locations within the cardiovascular system. For example, catheters can provide access to the central regions of the cardiovascular system in the vicinity of the high volume blood flow passageways immediately interconnected with the heart.
Cardiovascular access catheters typically include an elongated, flexible catheter tube having one or more fluid flow passageways, or lumens, extending longitudinally therethrough to an open end of the catheter. During implantation in the body of a patient, the open end of the catheter is inserted through an incision in the skin into a blood vessel of the cardiovascular system. This inserted end is referred to as the distal end of the catheter, while the opposite end is referred to as the proximal end of the catheter. The distal end of the catheter is advanced through the blood vessels of the cardiovascular system to a predetermined location at which intended therapeutic activity is to be conducted. The portion of the length of the catheter proximate the distal end thereof resides in contiguous blood vessels of the cardiovascular system. The catheter extends through an incision in the skin of the patient at a location remote from the predetermined location at which therapy is conducted and remote from delicate viscera. An extracorporeal portion of the catheter, which includes the proximal end, is located outside the body of the patient and is accessible to medical practitioners. Medication or nutrients are introduced into the proximal end of the catheter and delivered to the predetermined location in the body of the patient through the open distal end of the catheter body. The open distal end of the catheter body provides a permanent opening through which fluid communication is continuously maintained between the lumen or lumens in the catheter body and the cardiovascular system of the patient.
When the catheter is being used for therapeutic purposes, it is necessary to establish continuous fluid communication through the catheter between the proximal end of the catheter and the interior of the body of a patient. When the catheter is not being used, however, this continuous fluid communication is undesirable and dangerous. The pathway along which this continuous fluid communication is established provides a route by which infection can enter into the body of the patient. The pathway is also a conduit through which fluid can uncontrollably escape from the cardiovascular system of the patient, or through which air can enter into the cardiovascular system of the patient. Therefore, the continuous fluid communication to the cardiovascular system provided by the catheter must be curtailed when the catheter is not in use.
One method of curtailing the continuous fluid communication provided by the catheter involves clamping the extracorporeal portion of the catheter body with a tube clamp. A tube clamp can impose undesirable wear on a catheter body and may be released unintentionally. In addition, while a tube clamp prevents net fluid flow through the catheter, a tube clamp does not prevent fluid transfer between the cardiovascular system of the patient and the lumen of the catheter body through the open distal end thereof. The lumen of a cardiovascular access catheter is filled with a relatively static column of fluid when the catheter is not in use. If a catheter has a permanently open distal end, constituents of body fluid diffuse into that column of fluid through the open end when the catheter is not in use, even though access to the cardiovascular system through the catheter has been curtailed by clamping the extracorporeal portion of the catheter.
Small volumes of blood might enter the stagnant column of fluid and clot, possibly leading to various complications that are dangerous to the patient. The clotting process can completely obstruct the otherwise permanently open distal end of the catheter or the interior of the associated lumen. An obstruction renders the catheter useless and requires removal of the obstructed catheter and implantation of a replacement catheter. When the catheter lumen is only partially obstructed by the clot, the risk to the patient can be severe. Fluid forced through a partially obstructed lumen may flush the clot out from the lumen into the cardiovascular system of the patient. Inside the cardiovascular system, the clot can obstruct blood vessels and contribute to a heart attack, a pulmonary embolism, or a stroke.
To minimize the dangers associated with clots, cardiovascular access catheters have been provided with closed distal ends and selectively operable valve structures formed through the catheter body near the distal ends thereof. These valve structures open during therapeutic fluid infusion or aspiration, but remain closed when the catheters are not in use. A valve structure developed for this purpose takes the form of a longitudinally extending planar slit formed through the outer wall of a catheter tube having a closed distal end. The slit extends from the exterior of the catheter through the closed distal end or through the circumferential outer wall of the catheter body to a lumen in the catheter body. On either side of the slit, portions of the outer wall of the catheter body are formed by the slit into a first valve wall and a second valve wall. The first valve wall terminates at the slit in a first slit face. The second valve wall terminates at the slit in a second slit face that is congruent to the first slit face. When the valve is in the closed position thereof, the planar slit faces are opposed to and in abutment with one another, meeting in what will henceforth be referred to for convenience of discussion as a slit orientation plane. The opposed faces of the slit normally remain in abutting sealing engagement, isolating the column of fluid in the associated lumen from the region in the body of the patient outside the catheter tube in the vicinity of the slit valve.
FIGS. 1-8 depict a cardiovascular access catheter device 20 that includes such a known slit valve structure.
FIG. 1 is a perspective view of cardiovascular access catheter device 20 implanted in the body of a patient 10 for whom a therapeutic procedure is to be undertaken on an intermittent basis, by way of example, in superior vena cava 12 of the venous subsystem of the cardiovascular system. Catheter device 20 includes a soft, biocompatible, single lumen catheter body 22 having a distal portion 24 that is intended to reside in superior vena cava 12 and a proximal end 26 that resides outside the body of patient 10. A significant portion of catheter body 22 proximate distal portion 24 resides in the contiguous blood vessels extending away from superior vena cava 12. In the vicinity of shoulder 14 of patient 10, a section of catheter body 22 extends through an incision in the skin between the blood vessels and the exterior of the body of patient 10. Proximal end 26 of catheter body 22 carries a tubing clamp 42 and terminates in a luer connector 40 that can be selectively coupled to extracorporeal medical equipment.
Alternatively, proximal end 26 of catheter body 22 could be attached to a subcutaneously implantable access port, and the entire length of catheter body 22 and the access port could be implanted within the body of patient 10. In this configuration, the entire device is implanted in the body, and no extracorporeal portion is provided.
FIG. 2 is an enlarged plan view of distal portion 24 of catheter body 22 of FIG. 1. Catheter body 22 at distal portion 24 thereof is seen to have a longitudinal axis L22 and to terminate in a closed distal tip 34. Distal portion 24 of catheter body 22 has a cylindrical circumferential outer wall 28 and a semispherical terminal endwall 36 that is continuous with outer wall 28. A slit valve 46 is formed in outer wall 28 near terminal endwall 36. Slit valve 46 includes a planar slit 48 that extends longitudinally along outer wall 28 parallel to longitudinal axis L22 of catheter body 22. Planar slit 48 separates a first valve wall 50 from a second valve wall 52 that are otherwise integrally formed with outer wall 28 of catheter body 22, except at planar slit 48.
FIG. 3 is a transverse cross-sectional view of distal portion 24 of catheter body 22 illustrated in FIG. 2 taken along section line 3-3 shown therein. Outer wall 28 is seen to enclose a single lumen 38. FIG. 4 is an enlarged detail view of the portion of the cross section of FIG. 3 depicting slit valve 46. First valve wall 50 terminates in a first slit face 54, and second valve wall 52 terminates in a second slit face 56 that is congruent with first slit face 54.
Slit valve 46 functions as a reliable two-way, three-position valve. In the closed position of slit valve 46 shown in FIGS. 2 and 3, fist slit face 54 and second slit face 56 of slit valve 46 are in abutting and sealing engagement. Fluid is precluded from entering or exiting lumen 38 of catheter device 20 through slit valve 46 in the closed position of slit valve 46.
To move slit valve 46 into an outwardly open position, positive pressure is applied to the static column of fluid occupying lumen 38. This pressure creates a positive pressure differential between lumen 38 on one side of slit valve 46 and the region in the body of patient 10 on the other side of slit valve 46. FIG. 3 illustrates outwardly-directed forces Fo acting on outer wall 28 of catheter body 22 that are generated by the positive pressure differential. FIG. 4 illustrates that in the process depicted in FIG. 3, a circumferentially applied tangential tensile stress σTt is generated in outer wall 28 by forces Fo. Tangential tensile stress σTt causes first slit face 54 and second slit face 56 to separate out of abutting, sealing engagement in the manner shown in FIG. 4. Once first slit face 54 and second slit face 56 are out of abutting, sealing engagement, forces Fo cause first valve wall 50 and second valve wall 52 to open outwardly as shown in FIG. 5 into the outwardly open position of slit valve 46. Fluid 64 is infused from lumen 38 into the cardiovascular system of patient 10 as shown in FIG. 5 due to the positive pressure differential. If the pressure differential between lumen 38 and the region in the cardiovascular system of patient 10 on the other side of slit valve 46 is reduced to a threshold level, first slit face 54 and second slit face 56 will again assume the closed position of slit valve 46 shown in FIG. 3 and resume abutting, sealing engagement.
To move slit valve 46 into an inwardly open position, a negative pressure or suction is applied to the static column of fluid contained within lumen 38 from proximal end 26. This suction generates a negative pressure differential between lumen 38 on one side of slit valve 46 and the region in the body of patient 10 on the other side of slit valve 46. FIG. 6 illustrates inwardly-directed forces Fi acting on outer wall 28 of catheter body 22 that are generated by the negative pressure differential. Slit valve 46 is shown in the closed position thereof in FIG. 6. FIG. 7 illustrates that in the process depicted in FIG. 6, a circumferentially applied tangential compressive stress σTc is generated in outer wall 28 by forces Fi Forces Fi cause first valve wall 50 and second valve wall 52 to open inwardly as shown in FIG. 8 into the inwardly open position of slit valve 46. Fluid 66 is aspirated into lumen 38 from the cardiovascular system of patient 10 as shown in FIG. 8 due to the negative pressure differential. If the negative pressure differential is reduced to a threshold level, first slit face 54 and second slit face 56 will again assume the closed position of slit valve 46 shown in FIG. 6 and resume abutting, sealing engagement.
At the extreme ends of slit valve 46 shown in FIG. 2, opposed first slit face 54 and second slit face 56 meet at a proximal slit end line 58 and a distal slit end line 60 shown on end in FIG. 2 that extend radially through catheter body 22. The extreme ends of slit valve 46 do not separate during aspiration or infusion. Thus, the inward or outward deflection of first valve wall 50 and second valve wall 52 of slit valve 46 occurs, not to a uniform extent along the length of planar slit 48, but to an extent that ranges from a maximum at the center of the length of planar slit 48 to a minimum at a distance away from that center in the direction of each of proximal slit end line 58 and distal slit end line 60.
The development of a reliable two-way, three-position slit valve formed in the circumferential outer wall of a catheter has solved many problems associated with catheters having permanently open apertures in the distal end of the catheter body that resides inside the cardiovascular system of the patient.
Historically, cardiovascular access catheters with slit valves have been made from medical grade silicone materials. Silicone materials are soft, flexible through a wide range of temperatures, and free of clinically harmful, leachable plasticizers. Silicone materials are resistant to chemicals, relatively non-thrombogenic, and atraumatic to surrounding tissues, all of which contribute to high biostability and biocompatibility. In addition, silicone materials may be sterilized by ethylene oxide gas, gamma or electron beam radiation, or steam autoclaving.
A catheter must have sufficient wall thickness to prevent tearing or bursting during use. Catheters are susceptible to tearing during insertion into or removal from the body of the patient. In addition, the portion of the catheter implanted in the body of the patient can tear at certain locations where the catheter is subjected to localized stress within the body. The extracorporeal portion of an implanted catheter can tear due to mishandling. Catheters also are susceptible to bursting when fluids are injected through the catheter under pressure. Susceptibility to bursting increases when the lumen of the catheter has become occluded at some point along the length of the catheter.
Recently, open-ended cardiovascular access catheters also have been manufactured from polyurethane materials. Polyurethane materials have certain mechanical properties that contrast positively with those of silicone materials. Polyurethane materials have good tensile and tear strength. A catheter constructed from polyurethane material is typically more durable than a similarly sized catheter constructed from silicone material. A catheter constructed from a polyurethane material having a predetermined tensile strength may have a wall thickness that is less than the wall thickness of a catheter constructed from a silicone material having equal tensile strength. Fluid flow rates through a catheter lumen are proportional to the cross-sectional area thereof. The cross-sectional area of catheter lumens can be increased in catheters in which the outer wall thickness can be reduced. A cardiovascular access catheter constructed from a polyurethane material, therefore, can exhibit increased fluid flow rates relative to a similarly sized silicone catheter.